Can anyone from the region comment on the status of plans for the landside linkup on the German side? Last time it made the press it was because the project was at risk of seeing the Danish tunnel finished before Germany could tell not even when but if a linkup would ever make it across bureaucratic hurdles. Almost like a Darien Gap made exclusively of red tape.
BretonForearm 18 minutes ago [-]
That horrible website overrides web page scrolling and disables pinch zoom. Bad!
Here's a similar video for BART's Transbay Tube, which was built in a similar way.[1] The major differences come from building in an earthquake zone. The Transbay Tube is mostly steel, rather than concrete, for flexibility. There are expansion joints. And the Transbay Tube sits on a gravel and sand base rather than hard rock, on purpose.
The Transbay Tube sections were built in the Bethlehem Steel shipyards in San Francisco.
A museum opens this month to commemorate that shipyard. It's in Dogpatch in SF, if you know the area. The shipyard still has a submersible drydock, but it hasn't worked in ten years and will be demolished soon, hopefully before it sinks.
The SF Bay Area once had far more heavy industry than most people realize.
It's not in an earthquake zone, but isn't the Scandinavian continent still rising at a surprisingly fast rate? I wonder if that could affect the engineering of the Fehmarnbelt tunnel, in an "in x years one end of the tunnel will have risen n centimeters compared to the other end" way. It's probably such a small amount it's well within levels where regular maintance will cover it anyway, but I'm still curious.
jedberg 2 hours ago [-]
Today I learned the Transbay Tube is the longest immersed tube in the world. Given that it opened in 1974, it presumably has held that record for 52 years!
Liftyee 9 hours ago [-]
I'm amazed that engineers can make submerged tunnels work and that leaks don't (literally) sink the whole plan.
ianburrell 8 hours ago [-]
The Transbay Tube carrying BART across the bay is immersed tube. The sections were welded together by divers. The sections were filled with water and then pumped out.
Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.
imglorp 8 hours ago [-]
A video posted in another thread says the segments are sealed with bulkheads, floated into position, submerged by allowing water into a ballast section, dropped into place , aligned with pins, drawn to the next segment with hydraulic jacks, and sealed to it with rubber gaskets. Then the bulkheads can be removed. The gaskets also allow for some thermal expansion.
I'm curious what the lifetime of those gaskets might be and how you might maintain them.
poizan42 2 hours ago [-]
They are GINA gaskets[0], they were supposed to last 120 years[1], but it has recently been shown that they may deteriorate faster than previously expected due to being under constant compression[2][3]
The "ballast sections" may act as bilges, so that any leaks will accumulate there and can be pumped out. 100% water-tightness is not essential. Occasional re-grouting/caulking of the joints may be good enough.
bobthepanda 7 hours ago [-]
I figure once you join them, you could also apply waterproofing to the outside as well, no?
lmm 7 hours ago [-]
Maybe. What would that look like, adding more gaskets on the outside? That sounds even harder to maintain since the only way to get access is diving.
euroderf 6 hours ago [-]
Some kind of goop that would get very slowly squeezed into gaps by water pressure ?
usrusr 10 minutes ago [-]
Sealing is really not that difficult if you have access to the high pressure side. The hard part is identifying the location of the leak. In sum, this means that they have to absolutely nail it, on the first attempt, for the bottom part that is resting on the sea floor. If they can to that, the rest of the circumference will also be so good they don't have to even think about fixability.
6 hours ago [-]
bloggie 5 hours ago [-]
Here’s a fun video about how one sunken tunnel was built in Vancouver back in the 50s. https://youtu.be/A1igKk8eK0M
readthenotes1 9 hours ago [-]
52.6B krone for 18 km
8B USD for 11 miles
CACHSR IOS 36B USD for 171 miles.
The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course
lukan 17 minutes ago [-]
The building of this tunnel will likely create way more CO2, than can be saved by providing a more direct route and avoiding ferries
(german source ... and very critical of the project)
Personally I like the concept of having a more direct access to scandinavia and see lots of other positive long term effects.
bradchris 8 hours ago [-]
Well, if we’re comparing CA infra costs, for a more 1-1 comparison you can look at the $9.7B Los Angeles is spending on building out a long-awaited subway line (phase 1 of 3 opened Friday!) and see how tunneling underwater looks like a bargain in comparison.
The Transbay Tube sections were built in the Bethlehem Steel shipyards in San Francisco. A museum opens this month to commemorate that shipyard. It's in Dogpatch in SF, if you know the area. The shipyard still has a submersible drydock, but it hasn't worked in ten years and will be demolished soon, hopefully before it sinks.
The SF Bay Area once had far more heavy industry than most people realize.
[1] https://www.youtube.com/watch?v=247JT7ctQ_I
[2] https://bethlehemshipyardmuseum.org/
Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.
I'm curious what the lifetime of those gaskets might be and how you might maintain them.
[0] https://www.trelleborg.com/en/marine-and-infrastructure/medi...
[1] https://www.trelleborg.com/marine-and-infrastructure/-/media...
[2] https://www.sciencedirect.com/science/article/abs/pii/S08867...
[3] https://dailygalaxy.com/2026/03/rubber-used-in-undersea-tunn...
8B USD for 11 miles
CACHSR IOS 36B USD for 171 miles.
The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course
(german source ... and very critical of the project)
https://www.nabu.de/umwelt-und-ressourcen/verkehr/verkehrsin...
Personally I like the concept of having a more direct access to scandinavia and see lots of other positive long term effects.
https://www.latimes.com/california/story/2026-05-07/los-ange...